This invention relates to heat-shrinkable products which can be employed as seals on damaged pipes and conduits and as insulation on damaged electrical conductors. More particularly, this invention relates to heat-shrinkable products which can function when no free end is available on the article to be protected. Such products are often referred to as wrap-around sleeves. The major obstacle in producing such a sleeve is the development of a closure device which can withstand the forces generated during shrinking at heat recovery temperatures.
U.S. Pat. No. 3,379,218 to Julian S. Conde discloses a heat shrinkable wrap-around sleeve whose closure consists essentially of button holes and buttons. This sleeve has the disadvantage of not being fabricated by the inexpensive extrusion method, but by the more expensive molding method. A further disadvantage of this sleeve is that, of necessity, the button holes and buttons are constructed of the same material as the heat-shrinkable portion. As such, when the sleeve is heated to soften the heat-shrinkable portion for recovery to take place, the button holes and buttons may soften sufficiently so that the closure might fail.
U.S. Pat. No. 3,455,336 to Roger H. Ellis discloses a heat shrinkable wrap-around sleeve whose closure consists of elongated ridges along its edges and a metal channel which slips over the ridges thus engaging the edges. The use of a metal channel has many disadvantages. In order to effect a closure, the long metal fastener must be slid over the two elongated ridges. This is a rather difficult operation, particularly if the closure is a long one. The weight of the wrap-around sleeve tends to pull the two ridges apart before the metal fastener can be slid over them. Further, the fastener can get stuck easily. Also, the resulting closure is a raised strip along the sleeve covered with a metal fastener. If another cable is near the closure, the metal would rub against it causing damage. If the repaired cable has to be moved, the raised metal portion might catch on edges or other obstructions. If the repaired cable is rolled and unrolled as is the case with mine cables, the metal portion would rub against other parts of the cable, causing wear, would tend to catch and would be a safety hazard if it struck a miner. Furthermore, the metal in some instances might cause electrical problems with the cable or other electrical equipment. Some of the problems with the raised metal closure can be overcome by removing the metal fastener. However, after recovery of the sleeving, the fastener is so tightly held in place that it cannot be easily slid off. The alternative is to cut off the protuberances with the metal fastener as well. Not only is this an added time consuming step, but should the repairman cut into the sleeving itself, then the entire repair is useless.
U.S. Pat. No. 3,530,898 to John R. Wilson discloses a heat shrinkable wrap-around sleeve whose closure consists of edges with a plurality of loops and a metal rod which is passed through the loops. This sleeve has the disadvantage of requiring that the body of the sleeving must be cut and folded to produce the loops. A metal rod is required to hold the closure together with the resulting problems as described in regards to the Ellis Patent. But, perhaps the greatest disadvantage of this sleeve is the extreme difficulty encountered when inserting the rod into the loops, especially when the closure is a long one.
U.S. Pat. No. 3,574,313 to Ken Tanaka discloses a heat shrinkable wrap-around sleeve whose closure consists of slots on one edge and preshrunk babs on the other edge. The preshrunk tabs on one edge are inserted into the corresponding slots on the other edge to form the sleeve. This sleeve has the disadvantage of the Conde closure in that the slots and tabs are constructed of the same material as the heat-shrinkable portion. As such, when the sleeve is heated to soften the heat-shrinkable portion for recovery to take place, the slots and tabs may soften sufficiently so that the closure might fail. However, the greatest disadvantage of this sleeve is the extreme difficulty in inserting all the tabs into all the slots especially in a long closure where tabs may slip out of slots while other tabs are being inserted into other slots.
U.S. Pat. No. 3,770,556 to Joseph H. Evans and Gareth W. Will discloses a heat shrinkable wrap-around sleeve whose closure consists of edges which overlap and have been coated with a contact adhesive. To prevent the overlapping edge from peeling back during recovery a restraining member consisting of a metallic foil coated with contact adhesive is adhered to the overlapping edge. This sleeve overcomes many of the disadvantages of the previously-mentioned sleeve. It is simple for the manufacturer to fabricate. It does not require the use of metal fasening devices. It does not relay on the same material as the heat-shrinkable portion of the sleeve for the closure device. However, it overcomes these disadvantages by requiring the user of the sleeve to fabricate in effect his own closure system. This sleeve requires that the user apply contact cement to the two edges of the heat-shrinkable member as well as to a sheet of material used to prevent the edges from peeling back. Should the manufacturer apply the contact cement, then the user is required to use solvents or heat to reactivate the adhesive.
Said U.S. Pat. No. 3,770,556 includes a review of the disadvantages of certain prior-art patents and patent applications, including those hereinabove mentioned. Since said U.S. Pat. No. 3,770,556 is assigned to the assignee of said prior art patents and patent applications, said review of their disadvantages is presumably authoritative. Said U.S. Pat. No. 3,770,556 states, at column 2 lines 13-15: "It had been thought that no adhesive could withstand the force exerted by a heat recovery step at the temperature of recovery," and asserts that the inventors named in said patent discovered that some contact adhesives were potentially capable of withstanding this force, and that such adhesives can be used when peel-back tendencies are overcome.
Specific peel-back-prevention measures mentioned include the use of cross-linking or the use of additional strips of metal or other materials or the use of a thin outer edge. Specific contact adhesives include chloroprene based polymers such as neoprene. All the claims of this patent require separate peel-back prevention means.
In reviewing said prior art patents in the Amendment dated Oct. 10, 1972 and filed Oct. 12, 1972, the applicants in said U.S. Pat. No. 3,770.556 assert (at page 4 thereof): "As pointed out in the Specification of this application, many solutions were found that would provide a suitable wraparound sleeve; however, they all required some mechanical connection between the split edges of the sleeve to enable the sleeve to withstand the substantial forces exerted by the heat recovery of the sleeving material. It is the presence of the effects of recovery that would, and apparently did, dissuade those skilled in the art from attempting to use an adhesive to bond together the two edges of a split sleeve. The effects of recovery are manifested in two ways: first, a substantial shearing force is exerted in the area where the edges of the split sleeve are brought together; second, the uppermost edge of the sleeve tends to peel upwardly and away from the underlying edge. As a result of these effects, the workers in the prior art believed that a mechanical connection was necessary. We submit that it would not be at all obvious to one skilled in the art that an adhesive system could be provided that would withstand these two divergent effects of heat recovery, and withstand them at temperatures approaching 200.degree. C. where adhesive bonds are normally weakened but where a heat recoverable sleeve is typically heated to cause recovery. It was only the applicant's recognition that a specific adhesive system, namely, a contact adhesive, when used in conjunction with means for preventing peel-back, could provide the solution that previously eluded workers skilled in the art.
"Turning now to the claims, all elected claims 3, call for a heat recoverable closure member having areas of a contact adhesive together with means to prevent peeling back of the sleeve. When the closure member is placed about a conductor or other longitudinal member, the areas of contact adhesive may be simply brought together to form a secure bond. None of the patents cited by the Examiner disclose a contact adhesive in any form and, instead, show pressure sensitive or other adhesives which would weaken with heating.
"Contact adhesives are not the same as pressure sensitive adhesives. Pressure sensitive adhesives, typified by the type of adhesives used on adhesive tape or cellophane tape have the characteristic of being sticky to the touch. In contrast, contact adhesives may exhibit little or no stickiness or tackiness until touched with another layer of contact adhesive. Such adhesives are typically applied to each of the two surfaces to be joined and allowed to dry to a relatively tack free state. These two surfaces are then brought together, at which time a tight bond is formed. Thus, they exhibit autoadhesion or the ability to stick to themselves. In contrast, pressure sensitive adhesives will stick to most surfaces and feel sticky to the touch. Contact adhesives are defined in applicants' Specification at page 13, lines 5 through 15 and particular base polymers and formulations are described in the Specification on pages 13 through 19.
"Turning now to the prior art of record, the patent to Carlson suggests the use of a "pressure sensitive adhesive tape" (see Carlson column 1, lines 62-64). Such a tape would not maintain strength at the elevated temperatures necessary to bring about heat shrinking. Thus, if a person faced with applicants' problem of providing a wraparound closure sleeve were given the Carlson reference, he would find that the resulting sleeve would pull apart upon heating. It will now be shown that the secondary references do not supply the deficiencies inherent in the Carlson reference when adapted to applicants' use . . . "
The foregoing excerpt from arguments made by the applicants of U.S. Pat. No. 3,770,556 show that, until the present applicant's invention disclosed and claimed herein, it was thought that pressure sensitive adhesives were inoperative for use with heat-shrinkable materials.